Bike Won't Idle

[Jimmyshifts]

I completely disassembled my carbs and cleaned them. The bike wouldn't run before I did that. Now it runs strong but only above 3k rpm. To get it started I have to use the choke. Once it starts I rev it up and I can let the choke go as long as I stay above 3k. When I put the idle screws in I tightened them all the way then backed them out 1.25 turns. Do you think the problem is with the idle screws or with the carb sync? It looks like the butterfly was closing completely so I gave them a small turn.

Thanks!!

[thewiz]

Of course, Jimmy ...

as you may imagine, carb questions often dominate this forum. There has been much written and there are a TON of knowledgable carb guys on here, amoung them, I'm probably the least. Don't know what your mechanical background is, but for the uninitiated, there is most often a pretty steep learning curve to dialing in carbs and lotsa' extra R&Rs , but here are some places to start. If you haven't already done this, begin by reading and digesting ALL of the carb tech tips in that section of the Forums.

I'm a big believer in the logical process when diag'ing problems ... 'sharp shooting' is usually only marginally effective for me. The symptoms you've described are common when there is a huge vacuum leak and/or carbs out of synch or a even a non functioning pilot circuit. A quick check for a vacuum leak would be to start it up and get it running as slow as you can then, while running, spritz some WD40 or carb cleaner all around the intake manifold areas and diaphram areas. If the RPM jumps up, there is a vacuum leak. Cure it and proceed. If this isn't the problem or the ONLY problem .... read on

You didn't mention the condition of the other parts involved like idle mix screws, inlet screens, float needle and seats, floats, needle jets, and slide needles and diaphrams and so on. Maybe you could give us a little more detail about what you observed when the carbs were apart and the process you used for the actual cleaning itself, bench synching and setting float levels. That will help these guys to help you better.

[foreda]

Sync

Did you bench set using the bread tie method before installing. When you sync, you will need to readjust the idle screw until you get it right.

[DiverRay]

How tight did you turn down the screws??? You only need a LIGHTLY SEATED on them. If you tightened them down, you may have broken the tips off of all 4 screws!
Do a search if you did, the fix isn't easy or pretty.
A quick check would be to remove the screws one at a time and look at the tip. they should have a sharp needle point on them. If not, the tips are probably stuck in the carb bodies, and you have no mixture control for idle.

[CatatonicBug]

Remember that the pilot jets are what feed the carb up until about the 3k range. After that, the main jets kick in. Something tells me that your didn't clean the carbs completely, and the pilot jets are clogged. Looks like your choke circuit is working, so that part may be ok, but once it's warmed up you should be able to push in the choke, and have it idle at 1100 RPM with no problems.

Take the carbs out again, clean out the pilot jets and their circuit. While you're in there, double check the choke port in the bottom of the float bowl. It gets clogged easily, and is easily missed by newbies (I know, 'cause I did it myself ).

[Jimmyshifts]

More Detail

Thanks Guys,

Let me try and provide some more detail. I really appreciate all your help. I've cleaned the carbs about ten times be now. I started out not knowing anything. Now I know just enough to get into trouble. I have plenty of general knowledge but I'm getting out of my comfort zone when it come to float bowl height, etc...

I can't find any vacuum leaks, When I got the bike the carbs were gummed up pretty bad. I cleaned them and found a stripped idle screw with the needle mashed all the way down. I had to take it to a machine shop to have it extracted. I bought 4 new idle screws and was very careful not to over tighten them.

So if I need to adjust the carbs how come there are only three screws? How do I get the other butterfly to open?

Are the idle screws so sensitive that if I open them to much that it would have the same effect? How much should I turn each time?

On anther note... does anyone recommend a place around Philadelphia that I can get my bike inspected at, or other work that might need to be done?


Thanks!!!

[foreda]

Carbs

Thanks Guys,

Let me try and provide some more detail. I really appreciate all your help. I've cleaned the carbs about ten times be now. I started out not knowing anything. Now I know just enough to get into trouble. I have plenty of general knowledge but I'm getting out of my comfort zone when it come to float bowl height, etc...

I can't find any vacuum leaks, When I got the bike the carbs were gummed up pretty bad. I cleaned them and found a stripped idle screw with the needle mashed all the way down. I had to take it to a machine shop to have it extracted. I bought 4 new idle screws and was very careful not to over tighten them.

So if I need to adjust the carbs how come there are only three screws? How do I get the other butterfly to open?

Are the idle screws so sensitive that if I open them to much that it would have the same effect? How much should I turn each time?

On anther note... does anyone recommend a place around Philadelphia that I can get my bike inspected at, or other work that might need to be done?


Thanks!!!

In the sync process, the number 3 carb vac is what all the other carbs should be set to. Check out the carb tips in the "Tech Tip" forum.

[Jimmyshifts]

idle update

Hey guys,

I was getting already to tear apart the carbs again when I thought I would take it for a ride. I had to keep it above 3k rpm. After awhile I pulled up to a light and it was idling!!!! Maybe the bike needed to heat up or something got dislodged. Either way I'll take it. it still has some low end hesitation but at least its a start. I can tell it still needs some adjustment. MAybe one cylinder is doing more work or something. Well on to the next problem!!! Thanks guys!!

[thewiz]

Ok, Jimmy ... let's sort this out ..

First of all, what is the year and model? Not all XS carbs are exactly the same.

Sounds like what you're describing that you see only 3 of are actually the screws used to synch the carbs. The fourth one that you don't see is the big 'thumb wheel' looking screw and it is on the 'master carb'. The idle mixture screws are set vertically, higher than the synch screws with a visible spring underneath or in a recess with no visible spring depending on the year. The idle mix screws control the amount of fuel that gets let out to burn when the bike is idling. The synch screws move the butterfly or throttle valves open or closed. In order for the motor to idle good or do much of anything at all smoothly, the throttle valves must be set the same so that they all work exactly together ... that is called "synching" or synchronizing the carbs ..make any sense so far?

Float height is set with the carbs upside down and level with the bowls off. When looking at the float pontoons, take a metal shop rule or a dial caliper and measure from the where the gasket (the gasket should remain on the float bowl and not the carb body) would seat on the carb body to the highest point on the float pontoon. Should be roughly 1 inch or very slightly less. Like the butterfly valves, all the floats must be adjusted EXACTLY the same for the carbs to work correctly.

Next, bench sych the carbs with a bread tie ... do a search on 'bench synch' with a bread tie wire and do as the thead says. That will get the throttle valves all working pretty much together. Hate to say this, but there isn't any shoutcut that I know of to getting carbs to work right.

Do the two things above (float height and bench synch), but don't put the carbs back on yet and report to us when you're done. We can't do it for you from HERE ..cuz we ain't there ... so you will need to put forth a careful, thoughtful effort ... otherwise you're in for a very long, and probably unproductive and misreable experience.


Once again, if you'd like to make it much easier on yourself ... read all the Tech Tips on carbs and try to understand them and at least learn what parts are what, it will be time well spent and a hell of a lot less frustrating and time consuming than R&R ing the carbs 10 or 20 more times. Trust me.

Oh yeah ... is Wagner's Ballroom still there at Broad and Olony?

[DGXSER]

If I am reading correctly.....

Sounds like you have not tuned the idle mixture at all. What I read is you set the 1-1/4 turns out for your idle mix screws and left them there...done. You will need to adjust them to get the best running for each cylinder.

Also, the choke/enricher should be left on until the bike is warmed up. In the summer weather we have around my part of the world now, I leave my choke on for about 1/2 mile or so, in the winter takes longer for sure.

Like Wiz stated, the three screws you saw sound like the synchronizing screws. The bread tie synch just sets them to be equal. A true synch adjust the butterflys to provide equal vacuum draw form each cylinder at idle. This may and often does, require the butterflies to be slightly diff opening for each carb. A VERY small movment of the synch screw makes a BIG diff in the vac being drawn.

Again, like the Wiz described it, the idle screw is under the carbs and has a notched wheel on it, that sets your "master" idle speed after the rest of the tuning is done.

+1 on suggesting you read ALL of the carb related tech tips! ALOT of great info there.!!